In many applications there is a need to transport a wide band RF signal in a context where space and external power are either limited or not available. Modulating an optical carrier with the wide band signal and transmitting the modulated carrier over a propagation path to a receiver is a widely applied technique. While conversion of an analog signal to digital form is also quite common in some applications, the current state of the art does not easily address sampling frequencies greater than 1 GHz along with high resolution. This is a significant disincentive to the use of digital technology. There are applications of RF transport which transport the RF signal in analog form. Examples are found in U.S. Pat. Nos. 5,253,309; 6,115,162; 6,510,255; 6,643,417; 6,996,345 and 7,660,491 as well as in US Patent Publication 2003/0030868 and LaGasse et al, “Bias-Free High Dynamic-Range Phase-Modulated Fiber-Optic Link” appearing in IEEE Photonics Technology Letters, v #9, #5, May 1997, pp 681-683.
Maintaining linearity in the transport process (i.e., especially in carrying out modulation and demodulation processes) is important for transporting the wide band signal with favorable Spur-Free Dynamic Range (SFDR). Some RF transport schemes use coherent modulation employing Mach-Zehnder (M-Z) interferometric technology or similar. Likewise some applications use coherent demodulation with concomitant reliance on interferometric technology.